In a conventional book binding process, signatures are formed by printed sheets folded one or more times, and a book block is formed by collating the signatures, and the book block is cut at a spine thereof, and glue is applied to the trimmed spine of the book block, and a cover is attached to the spine of the book block, and the covered book block is trimmed by a three side trimmer to form a book.
In the prior art, there are some book block forming apparatuses for collating signatures to form a book block.
For example, according to an apparatus disclosed in Patent Document 1, each of printed sheets is folded along travelling direction thereof two or three times
According to this apparatus, in order to avoid misalignment of the signatures in the book block, the signatures are adhered to each other, and thereby it is not necessary to align the signatures again in the subsequent process.
FIG. 5B is a side view of such book block. Referring to FIG. 5B, one side face K1 close to a glue-applied area forms a spine of a book block K, and the opposite side face K2 forms a fore edge of the book block K.
In the subsequent process, as shown in FIG. 5C, the spine K1 of the book block K is cut, glue is applied to the spine K1 and a cover V is attached to the spine K1 through the glue. Thereafter, the book block K with the cover V is trimmed at the fore edge K2 as well as top and bottom edges thereof so as to be shaped into a book.
However, the book manufactured in such a manner has disadvantage that readers have trouble opening the book because glue joints w formed between signatures M during formation of the book block K are left in back margins of the book.
Also, in the above-mentioned book block forcing apparatus, as shown in FIG. 5B, the signatures M are stacked in a manner such that a fold line n side (the spine K1) of the stack is thicker than the opposite side (the fore edge K2) of the stack, and consequently, the book block K whose spine K1 warps is formed.
Then when this book block K is pressed and so on in the subsequent process, the signatures M sometimes wrinkle because of warping of the spine K1, which leads to deterioration of book binding. This is noticeable when a book block has a large number of signatures.